Vacuum-tube amplifier



Nov. 5, 1924;

7 5 R o l. T m m $3 mm s W mm m w w w Y E W N r .(FQ G w m Wh m. WM, Aum .M U d I lnlv D w m BM ww M a To all whom it may concern.

Patented Not. 25,1924.

DAVID emmns, or GRASMERE, new YORK.

VACUUM-TUBE AMPLIFIER.-

Application filed September 19, 1922. Serial No. 589,108.

Be it known that LDAVID GniMns, a citi zen of the United States, and aresident of Grasmerc, county of Richmond, and State of New York, haveinvented certain new and useful Improvements in Vacuum-Tube Amplifiers,of which the following is a specification.

This invention has to do with high frequency signaling systelns,andrelates, more particularly, to radio and other high frequency receiving,amplifying and repeating systems and circuits therefor.

In so-call'ed vacuum tube reflex circuits, particularly high frequencyreceivingcircuits as described in United States Patent No. 1,087,892,issued February 17, 1914, to Schloemilchand Von Bronk, and BritishPatent No. 132,668, issued to Marius Latour, as well as numerous otherpatents and publications, the same thermionic-vacuum tubes are utilizedto effect both radio frequency, and audio frequency amplificationsimultaneously. In the reflex systems comprising a plurality ofamplifying tubes heretofore known, the radio frequency amplification andaudio frequency amplification. were effected by the tubes incorresponding order of sequence. For example, let. it be assumed that areflex receiving circuit of the heretofore known type comprises threevacuum tube amplifiers and a detector. The incoming radio. frequencysignaling currents are impressed on the amplifier tubes successively inthe order 1, 2 3 and amplified by each tube, after which the amplifiedhigh frequency signaling current is impressed on the detector, fromwhich audible frequency current variations corresponding with thesignals are derived. The audible frequency currents are then impressedon the same amplifier tubes as before and likewise in the order 1, 2, 3.The amplified audio frequency currents are then impressed. on a suitableindicating device such as a loud speaking telephone.

From a consideration of the foregoing it will be seen that the firstamplifier tube has impressed upon it both. the weakest radio .frequencycurrents and the weakest audio frequency currents, while the thirdamplifiertube has impressed on it highly amplified radio frequencycurrents and highly amplified audio frequency currents. It follows thatwith such an arrangement the amplifier tubes are most unevenly loadedand that one tube may be very lightly loaded while another isoverloaded. To overcome the aforementioned disadvantage inherent inprevious reflex circuits and therefore to increase the efficiency ofoperation of amplifier tubes, is one of the principal objects of thepresent invention.

A further disadvantage greatly in evi:

Hence in previously known reflex circuits employing more than one stageof radio frequency amplification arises from the strong "tendency tooscillate at high frequencies.

This tendency comes about from the fact that even the most feeble radiofrequency oscillations whichmay be transmitted from the output side ofthe detector to the input side of the first amplifier tube through themedium of the intervenin audio frequency transformer or other audiofrequency path are generally so greatly reamplified by the succeedingtubes as to be sustained. This condition is of course likely to resultin highly undesirable beat notes and does in fact so result. Theelimination of the lastmentioned undesirable conditi'on is afurtherobject of'the present invention.

As in the known reflex circuits referred to, the present inventioncontemplates using the same vacuum tube amplifiers for effecting bothradio frequency amplification and audio frequency amplification, butinstead of passing the audio frequency currents through the amplifiertubes in the same sequence as the radio frequency currents, thusunevenly loading the tubes, the sequences are reversed, that is to say,the audio frequency amplification is effected by the amplifier tubes inthe inverse order or sequence as compared with the order or sequence inwhich the amplifier tubes are utilized for effecting radio frequencyamplification. By comparison with the explanation previously given, itwill be seen that a more even loading of the tubes is effected.

This results ,in materially increased efti ciency and improved qualityof tone repro duction arising from the reduction or elimination of tubedistortion.

The elimination or reduction of the tendency to sustain high frequencyoscillations is accomplished in the circuits of the present invention byreason of the fact that the out put of the detector is impressed on theinput circuit'of the last amplifier tube instead of one of the precedingtubes as heretofore,

and accordingly any high frequency oscilla-v tions which ma be tmimiaeafrom the .output of the detector totheiinput'of thelast amplifier tubethrough themed umof \the intervening audio frequencyfpath is ama plifiedby only one tube, been should be borne in mind that theienergyof theoscillations under consideration" is exceedingly small when impressedonthe input of the amplifier tube due to the attenuationof theaudio'frequency path, and that after a single stage of. amplification itis still very small. -'When these weak oscillations are furtherattenuated by the. succeeding audio frequency path through which theymust pass, if they pass at all, their energy is fur ther reduced to suchan-extent that they areincapable of being built up by the succeedingamplifier tubes to a sufiicient extent to 7 result in their beingsustained. The foreoing theoretical consideration appears-to econsistently borne out-by the results which havebeen'obtained inpractice. It it thought desirable to point out, however, that the samefactors have to be taken into consideration for the prevention of freeosexceed the negative resistance.

cillations as "in any vacuum tube-circuit arrangement wherein energy-maybe fedback from the output to the input circuit, namely, that thepositive resistance must words, the attenuation of the frequencyoscillatory energy must outweigh the effective amplification. If, then,vacuum tube amplifiers having high" amplification fac-' tors areemployed, the high frequency im pedances of the audio frequency paths(this refers more particularly to the mutual capacities' between thewindings of the audio frequency transformers-which capacities 40 .mustbe correspondingly low for high impedance to radio frequencies) must becorrespondingly high, but if the amplification factor is low, the highfrequency imped ances may be correspondingly low. Since the vacuum tubeamplifiers to be employed are usually decided upon in, advance, thecontrollable factor in the design resides in 1 the audio frequency path.The desired high frequency impedance, or, more specifically, low mutualcapacity between windings, maybe and generally is obtainable by properdesign of the audio frequency transformers without any ancillaryapparatus for increasing the high frequency-impedance being provi ed.

' For the purpose of distinguishing circuit arrangements according'tothe present invention, the term .inverse duplex has been coined andadopted. As may easily be im plied, this term refers to circuits whereinsome or all of the amplifier tubes are util-. i'zed for both radiofrequency and audio frequency amplication (thus dup'lex) and that thetubes are efi'ective .in the inverse order as already explained. Theterm in- In other quencies, but very high.

verse duplex therefore has a definite mean it is desired be scrupulouslyobing which served. i

In the following. detailed'de'scription of one of the preferredembodiments of the jects will be pointed out. I, I

The drawingshows a circuit diagram of an inverse duplex receiver-andamplifier comprising three amplifier tubes 1, 2 and 3 and detector. tube4; Each of the tubes is invention additional novel features and obof thethree electrode. type. including filacept that there-must be at leasttwo stages of radio frequency amplification and twostages of audiofrequency amplification. In some cases it may bedesirable to have onlytwostages'of audio frequency amplification and three stages of radio 3frequency, in

which event. any two of the amplifier tubes may be utilized for audiofrequency am plification; A number of other arrangements, may also bevresorted to'depending upon the total number of amplifier tubes and theamount of radio frequency and audio frequency amplification desired.

Conductors 17,-18 may'extend to a radio receiving system such asantennaand-ground respectively or to theterminals of a loop or they may connectwith a metallic trans mission l ne as in the case of so-called carriercurrent or wired radio telephone systems.

Variable condenser 16 is provided for tuning purposes, and is used, moreparticularly, when the apparatus is provided with I a loop antenna,which for the present purposes it will be assumed is employed.

The incoming ,high frequency signaling.

currents supplied by the loop are conducted through the medium ofcondenser ligand 1 conductor 57 to the grid 38 and filame iiti; 6.Condenser, 29 is designed topass the blocking audio frequency -current.weak high frequency current being amplified in the usual way in tube 1appears in amplified form in the high frequency outlet put circuit oftube 1, which includes plate 39, primary windiiw 50 of radio frequencytransformer 5, condenser 28 and filament 46. Condenser 28 is generall oflow capacity, providing a by-pass or high freimpedancc for low h gh;frequency currents while substantiallfyiflzo The minor? frequencies. Theadjacent-input and out-' putsides of succeeding tubes are interconnected through the medium of high frequency transformers 5, 6 and 7,each of which is designed to pass high frequency currents but to provideno path, or at most a very inefiicient path for audio frequenc currents.and 2 which are provided asby-pasSes for the high frequency currents areof such proportions as to greatly impede the passage of audio frequencycurrents. The high frequency currents are repeatedly amplified by theamplifier tubes in the order 1, 2, 3 and finally pass through the mediumof transformer 7 to detector tube 4. The input circuit of the detectortube includes a grid condenser and leak 37, the function of which iswell known."

The detector tube converts the super-aud-ible high frequency energy intoaudible frequency currents in the usual manner.

The output circuit .of the detector tube includes'plate 45, filament-49, battery 13 and primary winding 35 of the audio frequencytransformer 10. As previously stated, condenser 23 functions to bypassany high frequency currents which may appear in the output of thedetector, thus greatly reducing the energy of any high frequency current output which might be conducted to the primary winding 35oftransformer 10.

Amplifier tube 3, being the last in theseriesv of radio frequencyamplification steps, and therefore most heavily loaded at radiofrequency, is utilized for the firstaudio frequency amplification step.Secondary winding 34 of transformer 10 is accordingly connected totheinput'circuit of tube 3 in series with the secondary winding of radiofrequency transformer 6, conductor 59 and grid 42. The other endofsecondary winding 34 is connected to filament 48 through. contact 36 ofpotentiometer 15. The audio frequency current is therefore impressedacross the grid 42 and filament 48'and is amplified by-tube 3. I Theoutput circuit of amplifier tube. 3 in udes plate 43, primary winding 54of the radio frequency transformer 7, primary winding 3 of the audiofrequency transfo'rmeryf), batteries 13. 14 and filament 48 all inseries.

Secondary winding 32 of transformer iii-is connected with the inputcircuit-of the am plifier tube in the same manner as the sec' ondarywinding 34 of transformer 10 con-. nected with the input circuit ofamplifiertube 3.

The audio frequency input circuit ofamplifier tube 2 includes grid 40,conductor 58, secondary winding 51 of radio frequency transformer 55,secondary winding'32 of Condensers 23, 24, 25, 26

uen'cy current from the output I of amplier tube 2 to the input ofamplifier tube 1 is efl'ected, as in the preceding instances,

through the medium of audio frequency transformer 8 which includes aprimary winding 31 connected in the output/circuit of amplifier tube 2and secondary winding30 connected in the in ut circuit of amplifiertube 1. The seconc ary winding 30 is preferably, but not necessarily,connected, as shown, to one side of the filament 46 through conductor61." A direct connection between secondary "winding 30 and grid 38 ofamplifier tube 1 may be effected through the loop which would ordinarilybe connected to the terminals of conductors 17, and'18. In the event ofthe apparatus being used in conjunction with an ordinary antenna orametallic transmission line, the secondary coil of a variocoupler may beconnected across the terminals with the conductors 17- and 18, thusproviding a Cit path for the audio frequency currents in the inputcircuit of amplifier tube 1.

The audio frequency output circuit of amplifier tube 1 includes theplate 39, primary winding 50 of radio frequency transformer 5, asuitable indicating device 11 such as a loud speaking telephone,batteries 13 and 14 and filament 46.

so i

The iron cores of transformers 8, 9 and 10 are preferably grounded tothe output filaments as indicated, for instance, by con ductor 62. I

Filament resistances 19, 20 and 21- may be fined as indicated, and theirvalue is deter mined by the filament current requirements and thevoltage of the filament lighting battery 12. Resistance 22 is preferablyvariable on account of being associated with the detector tube 4, whichis more critical on filament temperature than are the amplifier tubes. 3

Since amplifier tube 1 effects the least radio frequency amplificationand, contra, the largest audio frequency amplification, and since thereverse is true of amplifier tube 3, it is evident that the load onthese two tubes tends to approach equality. The

sa -me'is apparently true with respect to amfplifientube 2, since theradio frequency and audig frequency loads, respectively. are in.-terinediate those carried by tubes 1. and 3.

By ireason'of this novel arrangement, it. is

found that the amplifier tubes may be operated with increased efficiencyand that the quality of the output is'materially' improved. It has beenexplained in a preceding paragraph how the circuit arrangement underconsideration is effective to suppress the formation of high frequencysustained oscillations, but a further explanation in' connection withthe circuit diagram is thought to be not out of order. Any highfrequency feedback from the output of detector tube 4 which may reachthe input of amplifier tube 3 must pass through transv former 10'.

Any high frequency leakage of this character is amplified by tube 3 andreturned, in part, to the input of detector tube 4 through transformer7, and, in part, to transformer 9', from'which it may be conveyed to theinput of tube 2, and, in turn, through transformer 8 to the input oftube 10 1. Sineethe attenuationat high frequencies of transformers 8,9and 10 is very high, the high frequency currents which maybe, fed backtherethrough are accordinglyv very weak. If the attenuation. of

It, transformer 10 due to the low mutual ca- Ell pacity between thewindings more than of sets the effective amplification of tubes 3 and 4,the high frequency oscillations under consideration cannot, besustainedby tubes 3 and 4: alone. Butit is-neeessaryto take intoconsideration-the possibility of some of the highfrequency currentleakage finding its way back asfar' as the input of tube 1, .and that,such being the case, all the tubes are available for re-amplification.Ina circuit comprising several tubes, the amplification and attenuationof high frequency leakage presents quitea complex situation which is noteasily calculated with accuracy, but the fact remains that if-theefiective attenuation of the audio frequency paths to the high frequencyoscillations is suflicient to more than offset all the effectiveamplification available to such high frequency leakage as may exist,there can-be no sustained oscillations set up. It is, therefore,essential to the best practice that the transformers 8, '9 and 10 bedesigned to provide sn'flicient attenuation at hi glrfrequencies e.,that 40 the mutual capacity between windings be sufficiently low) orthat some provision be made externally of the audio frequencytransformer for obtaining the necessary attenuation.

A further comparative advantage in the present system over theheretofore known reflex circuits arises from the fact that the telephone11 is connected to the output of the amplifier tube immediately adjacentthe loop. This provides only one stage of amplification for any audiofrequency disturbing currents which may reach the loop, such, forexample, as the cycle current ofneighboring electric light lines. It hasbeen found that a single stage of a1nplificarion is usually insufiicientto increase the intensity of low frequency disturbances to a point wherethey become materially noticeable, whereas with-two or three stages ofamplification, such disturbances may be of such strength as topractically obliteratethe signals. Although the explanation hereincontained concerning the theory of operation of the system described arebelieved to be correct, the invention is in no way dependent upon anaccurate understanding of the theory and should not be construed aslimited by such considerations. Neither is 'it essential to theinvention that the elements of the circuit be designed to preventsustained oscillations, although-that is generally thepreferred'practice.

' Having thus described my invention, what I claim and desire to secureby Letters Tatentis 1. A system comprising a. plurality of amplifiersarranged for interstage operation, I

.and circuit connections for said amplifiers,

said circuit connections bein so arran ed that sa1d amplifiers areoperable to ampl fy current variations of two different bandsoffrequencies, and means including said circuit connections whereby thecurrent variations. within one band of frequencies are impressed uponthe amplifiers in a predetermined order, and the current variationswithin the other band of frequencies are impressed upon the amplifiersin the inverse order as compared with the aforementioned predetermined.order. I

2. A multi-sthge amplification system comprising a plurality ofamplifiers, circuit connections for said amplifiers, the arrange- 'mentbeing such that superaudible high frequency current variations arerepeatedly amplified by said amplifiers in a predetera plurality of-saidamplifiers are rendered operable to repeatedly amplifythe audiblefrequency current variations from said rectifying means in the inverseorder as compared with the aforen'icntimwd predetermined order.

4. A multi-slagc amplilimu ion system comprising a plurality ofthermionic amplifiers arranged to repeatedly amplify modulatedsuper-audible high frequency current variations in a. predeterminedorder, means interconnecting said amplifiers operable to transmitsuper-audible high frequencycurrents with relatively high effi- MCIQHCYbut inoperable to transmit audible frequency currents to an appreciableextent, means for rectifying the amplified superaudible highfrequency'output of said amplification system. whereby audible frequencycurrent variations are derived, and means whereby a plurality of saidamplifiers are rendered operable to repeatedly amplify the audiblefrequency current variations from said rectifying means in the inverseorder as compared with the aforementioned predetermined order, saidlast-mentioned means being operable to transmit audible frequencycurrent variations with relatively high efficiency, but inoperable totransmit super-audible high frequency current variations-to anappreciable extent.

5. A multi-stage amplification system comprising a plurality .ofthermionic amplifiers and circuitconnections for said amplifiers, said.circuit connections being so arranged that said amplifiers are operableto repeatedly amplify current variations of two different bands offrequencies, and means including said circuit connections whereby thecurrent variations withinone band of frequencies are impressed upon theamplifiers in a predetermined order, and the cu'rrent'variations withinthe other band of frequencies are impressed upon the amplifiers in theinverse order as compared with the aforementioned predetermined order.

6. A multi-stage amplification system comprising a plurality ofthermionic amplifiers having input and output circuits and arranged torepeatedly amplifysuper-audible high frequency current variations inapredetermined order, one or more transformers operable to passsuper-audible high frequency currents with-relatively high efficiencybut inoperable to pass audible frequency currents to an appreciableextent, succeeding ones of said amplifiers being inter-connected in eachinstance through the medium of one of said transformers,- means forrectifying the amplified super-audible high frequency currents andthereby obtain-.

ing audible requency current. variations, means operable to'transmit theaudible frequency currents from said rectifying means to the inputcircuit of one of said amplifiers wherein the audible frequency currentvariations are amplified, and means operable to transmitv the amplifiedaudible frequency current from the output circuit of said lastmentionedamplifier-to the input circuit of another of said amplifiers whereinfurther audible frequency amplification is effected, said twolast-mentioned amplifiers being operable to amplify audible frequencycurrent variations in-the inverse order as compared with the order inwhich they are operable to amplify super-audible high frequency currentvariations.

7. In a signaling system, two thermionic amplifiers in cascade relation,input and output circuits for said amplifiers, a radio frequencytransformer having its primary winding connected in the output circuitof the first of said amplifiers and its secondary winding in the inputcircuit of the second of said amplifiers, a second radio frequencytransformer having its'primary winding in the output circuit of saidsecond amplifier, a rectifier, the secondary winding of said secondtransformer being connected in circuit with the saidrectifier, an audiofre-- quncy transformer having its primary winding connected with saidrectifier, the secondary winding. of said audio frequency transformerbeing connected in the input circuit of said second amplifier wherebylow frequency current variations derived from said rectifier areimpressed upon the input circuit of said second amplifier wherein theyare amplified, a second audio frequency transformerhaving its primarywinding connected in the'output circuit of said second amplifier and itssecondary windin in the input circuit of said first amplifier wherebythe audible frequency current variations are further amplified by saidfirst amplifier.

8. A system comprising a plurality of vacuum tube amplifiers eachincluding a cathode, an anode and a control electrode,

circuit connections for said amplifiers, said said last mentionedamplifiers amplify cur- I rent variations within said first mentionedband of frequencies.

4 9. A multi stage" amplification system comprising a plurality ofamplifiers, circuit connections for said amplifiers the arrangementbeing such that super-audible high he quency current variations arevrepeatedly amplified by said amplifiers in a predetermined order, andmeans whereby a plurality of said amplifiers are rendered operable torepeatedly amplify audible frequency currentvariations in the inverseorder as compared with the aforementioned predetermined order, both thesuper-audible and audible frequency current variations beingamplifiedsimultaneously. I

10. A malti-stage amplification system comprising a plurality ofthree-electrode vacuum tube amplifiers arranged to repeat.

edly amplify modulated super-audible high frequency current variationsin a predetermlned order, means, interconnecting said amplifiers,operable at relatively high efficiency to transmit su er-audible" highfrequency currents but at ow'efliciency to transmit audible frequencycurrents, a three-electrode vacuum tube detector having its inputelectrodes connected to the output end of said amplification system, andmeans whereby a plurality ofsaid amplifiers are rendered operable 'torepeatedly amplify the audible frequency current variations fromsaiddetector I in the inverse order as compared with the aforementionedpredetermined order, said last-mentioned means being operable atrelatively high efficiency to transmit super-audible high frequencycurrents.

' ther amplification in each successive step.

5 12. The method of signal reception and amplificatidn which consistsimpressing modulated .high frequency sigaling -current on a plurality ofamplifiefs m seriatign and effecting further amplification in eaclrs'ucqcessive step, convert ng the amplified hi b frequency signaling currentinto audib e1 frequency signaling current, impressingtlfe' audiblefrequency signaling current on the y same amplifiers in' seriatim but'in the :iii'iverse orden and effecting further amplifica -tion of, theaudiblefrequen'cy currents in;

each successive step.

13. The method of utilizing vacuum tubes as amplifiers,-whi'ch consistsin utilizing the "1 tubes in a predetermined sequence for repeatedlyamplifying high frequency varia-[ tions, rectifying the amplified high.frea quency variations thereby obtaining-lower frequency variations,andsubsequently uti lizing tne same tubes in inverse sequence forrepeatedly amplifying the ,lower frequency variations,

Inwitness whereof, Ihave hereunto set my hand this 18 day of September,1922.

DAVID GRIMES/

